Planar light-wave circuits, also known as planar light-wave chips (PLCs), are optical devices having optical components and networks disposed monolithically within stack(s) of optical thin films and supported by a common mechanical substrate such as a semiconductor or glass wafer. PLCs are typically designed to provide specific transport or routing functions within fiber-optic communications networks. These networks are distributed over a multitude of geographically-dispersed terminals and commonly include transport between terminals via single-mode optical fibers.
Wavelength-division multiplexing (WDM) is a commonly employed technology within telecommunication systems that provides transmission of multiple optical signals on a signal optical fiber by using different wavelengths to carry different signals. In the WDM system, each optical carrier signal is transmitted within a narrow wavelength band centered around a center wavelength. Each band is commonly referred to as an optical channel and is generally characterized or referred to by a single center wavelength (λx).
Within communication systems, chromatic dispersion in an optical fiber or within other optical components limits pulse propagation distances and/or bit rates. Dispersion is generally wavelength-dependent and causes a broadening of the optical signal as it propagates along the length of the optical fiber. Different wavelengths travel at different speeds along the length of the optical fiber, and as signals broaden due to dispersion, it may become difficult to distinguishing one pulse from another.
Numerous attempts have been made to limit the negative effects of such dispersion. For example, ring resonators act as dispersion compensators. The effect of the ring resonator depends on the coupling value and the size of the ring. Generally, a wavelength near resonance will couple into the ring and circulate before coupling out of the ring. Wavelengths closer to the resonant wavelength spend a greater amount of time circulating within the ring, while “off-resonance” wavelengths spend little or no time within the ring. Effectively, this process compensates for dispersion by speeding up “slow” wavelengths that will spend little or no time within the ring resonator and slowing down “fast” wavelengths that will circulate multiple times within the ring resonator. Absolute time spent in the ring depends on the coupling value. Thus, adjusting the coupling value can adjust the magnitude of dispersion.
Across a system's operating band of signals, there is an average dispersion value and a slope component to chromatic dispersion. The average value and the degree of slope may or may not be related, and depend on the details of the system. For example, the average dispersion value and the degree of slope may be related in a communication system that is dominated by one type of optical fiber.